During normal development, vascular smooth muscle cells (VSMC) undergo differentiation from a proliferative phenotype characteristic of neonatal and embryonic vessels, to a contractile phenotype associated with adult vessels. In contrast to development of cardiac or skeletal muscle, VSMC retain much greater plasticity. In adult VSMC, phenotypic modulation resulting in changes in altered expression of a number of muscle-specific genes (SM-markers), results in cells with altered contractile, proliferative and migratory capacity. Transcriptional control of these genes occurs in response to multiple extracellular stimuli including circulating factors, extracellular matrix and mechanical forces. We hypothesize that phenotypic modulation requires sensing by VSMC of these multiple inputs, which integrate at the level of common signal transduction pathways. These pathways act on transcription factors, most critically serum response factor (SRF), that bind to the promoter elements of multple target genes. The goal of this proposal is to define these molecular signaling events and determine how they regulate transcription. During the previous funding period we have demonstrated that coordinated induction of SM-markers by arginine vasopression (AVP) is mediated through activation of the JNK and p38 family of MAP kinases. Induction by mechanical forces also involves these pathways. Conversely, PDGF suppression of SM-gene expression is mediated through activation of Ras and the PI3 kinase/Akt pathways. We have also demonstrated that growth of VSMC on matrices of different composition, through engagement of specific integrins and modulation of cytoskeleton, results in changes in expression of SM-markers. SRF is critical for regulation in all of these settings, and shows altered phosphorylation and subcellular localization. In this application we will focus on understanding the integration of signals generated by vasoconstrictors such as AVP, growth factors, and cell attachment resulting in alterations in gene expression. Three specific aims are proposed. Specific aim 1 will examine the role of MAP kinase and Rho family members in mediating the inductive effects of AVP. The second specific aim will define the mechanisms whereby Ras and Akt cooperate to mediate regulation of SM-gene expression by PDGF and redistribution of SRF. The final specific aim will examine the role of SRF phosphorylation in mediating control of SM-gene expression. These studies should provide a detailed molecular understanding of the events that control phenotypic remodeling in VSMC, and provide potential new targets for controlling this process in disease states.